Various kinds of coloring materials have so far been used for ink compositions for writing instruments.
Known are, for example, 1) black ink compositions for oil base ballpoint pens characterized by using a halochromic dye comprising principally a basic dye as a coloring agent (refer to, for example, a patent document 1), 2) oil base ink compositions for ballpoint pens prepared by using a reversible thermochromic composition comprising an electron-donating coloring organic compound which is a leuco dye, an electron-accepting compound, and a reaction medium for controlling the above color reactions (refer to, for example, a patent document 2), and 3) non-erasable ink compositions for writing instruments prepared by using a photochromic compound as a pigment (refer to, for example, a patent document 3).
However, when the above halochromic dye, leuco dye and photochromic compound are used as a coloring material for ink compositions for writing instruments, involved therein are the problems that they are still short of a solubility in the solvents of the inks and cause feathering and bleeding (transition of drawn lines) on the drawn lines and that the water resistance is not sufficiently high in a certain case.